1. Field of the Invention
The invention relates to method for manufacturing carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs are electrically conductive along their length, chemically stable, and each can have a very small diameter (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that CNTs can play an important role in fields such as microscopic electronics, field emission devices, thermal interface materials, etc.
Generally, there are three conventional methods for manufacturing CNTs. The first method is the arc discharge method, which was first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). The second method is the laser ablation method, which was reported in an article by T. W. Ebbesen et al. entitled “Large-scale Synthesis of Carbon Nanotubes” (Nature, Vol. 358, 1992, pp. 220). The third method is the chemical vapor deposition (CVD) method, which was reported in an article by W. Z. Li entitled “Large-scale Synthesis of Aligned Carbon Nanotubes” (Science, Vol. 274, 1996, pp. 1701). The CVD method is advantageously useful in synthesis of an array of carbon nanotubes and is advantageous in mass production, improved length controllability, compatibility with conventional integrated circuit process, etc.
Generally, the mainly used CVD method for making CNTs is the thermal CVD. FIG. 1 (related art) shows a schematic structure diagram of growth apparatus 100 using the thermal CVD to grow CNTs. The method using the growth apparatus 100 includes the following steps. Firstly, a heating furnace 101 is used to heat a reaction room 102, thus the temperature of the reaction room 102 reaches a pre-determined temperature to grow CNTs 108. The pre-determined temperature is in the approximate range from 500° C. to 1200° C. Secondly, a carbon source gas 103, which is mixed with a carrier gas, is introduced flowing over the catalyst film for growing the CNTs 108 on a substrate 104. Due to catalyzing by the catalyst film, the carbon source gas 103 supplied over the catalyst film is pyrolized in a gas phase into carbon units (C═C or C) and free hydrogen (H2). The carbon units are absorbed on a free surface of the catalyst film and diffused into the catalyst film. When the catalyst film is supersaturated with the dissolved carbon units, carbon nanotube growth is initiated. As the intrusion of the carbon units into the catalyst film continues, an array of carbon nanotubes is formed. Single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and the corresponding carbon nanotube array can be achieved by the above-described method.
In addition, there is a laser-induced chemical vapor deposition method (Laser-Induced Chemical Vapor Deposition, LICVD), which is an advanced method based on the traditional thermal chemical vapor deposition method. The advancement of LICVD is used a laser to replace the heating furnace 101. Thus, the CNTs can be grown at a fixed point and a low temperature by the LICVD.
With the continuous development of methods for growing CNTs, the CVD growth technology, in laboratory and large-scale industrial production, has matured considerably. Thus, carbon-nanotube-based field emission devices, electronic devices, thermal conductivity devices, and composite materials have been extensively investigated and gradually applied. The current apparatus for growing CNTs generally can only be used for growing carbon nanotubes. It cannot be used to observe the whole growth process of CNTs, and thus it is not easy to control the growth process of CNTs. In addition, how the growth of CNTs proceeds and how such applications may be integrated to reduce the growth process and the application process are major research issues nowadays, as such issues directly impact cost and time of production. A real-time method of positioning and/or monitoring in-situ growth is a potential solution to solve the above-described problems.
What is needed, therefore, is an in-situ method for growing carbon nanotubes that facilitates real-time positioning and monitoring during growth thereof.
Other advantages and novel features of the present apparatus for manufacturing carbon nanotubes will become more apparent from the following detailed description of present embodiments when taken in conjunction with the accompanying drawings.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one present embodiment for manufacturing carbon nanotubes, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.